When the dust settles on all of this, there will be a chance for those who by last night had turned Manchester into a sky blue sea to trace some title-defining moments from the 264 days which began when Sergio Aguero, a 60th-minute substitute, terrorised Swansea City and ended with him whirling around the same turf, shirt aloft.
Those fans will fix on how Vincent Kompany span away from Chris Smalling and Rio Ferdinand to deposit the header which won the league derby at the Etihad 15 days ago. Mario Balotelli's dismissal in the defeat at Arsenal on 18 April was certainly as significant, because it provided a way back into the starting line-up for Carlos Tevez, who has been iridescent in the six straight wins that wrapped up City's season.
Titles are won on pieces of serendipity like that. Not to be forgotten, either, are the three late goals in a 10-day period during April (Samir Nasri – 85th minute v Chelsea; Yaya Touré – 76th minute at Stoke, Aleksandr Kolarov – 86th minute v Sunderland) which allowed City to appropriate that age-old adage about the team from across town: "Football – 90 minutes of passing and then Manchester United win." Without just one of those three crucial goals, yesterday might well not have happened.
We must actually reach farther back. Mancini eulogises about the cold January Sunday when his side, three goals in arrears to United in the FA Cup third round, recovered with 10 men to a respectable 3-2 against United and grasped a belief that they could make up the "five-yard" mental deficit on the champions, much talked of by the Italian.
Sunday 23 October was vastly more important, of course. Sir Alex Ferguson claims that City's 6-1 Old Trafford derby victory that day came too early to matter and Mancini says that United's 10 men reduced its significance. Nonsense. It was a huge strike at the heart of the establishment that day and the reverberations from it were monumental.
There's also City's FA Cup semi-final defeat of United on 16 April last year, which punctured the aura of red invincibility and paved the way for what has come, though despite all the talk of that hallowed "winning mentality" and psychological edge, this is a story about pure commercial advantage. Purchasing a depth of ability, as the Abu Dhabi owners have done, has simply whittled away the percentages and reduced the potential for City failing to a level which not even Sir Alex Ferguson could ultimately match.
So while United have one striker better than any of Mancini's – Wayne Rooney and his 26 Premier League goals – City have three (Sergio Aguero, Edin Dzeko and Mario Balotelli) among the top 11 goalscorers. When David Silva's problems with a left ankle robbed City of his full powers, Nasri burst into his own for the first time.
And when Mancini's perennial nagging doubt about Micah Richards resurfaced during this finale, he turned to one of yesterday's goalscorers, Pablo Zabaleta, who, with Gaël Clichy, brings a dependability that Rafael da Silva and Patrice Evra have not provided across town.
Those two full-backs failed United in the 4-4 draw against Everton which brought us to where we were at 3pm yesterday. "Absolutely ridiculous", Ferguson has said of that Everton game, as if the defensive failings were a fluke, rather than the law of percentages being driven home.
A former member of Mancini's staff told me last week how Mancini asks his defensive coaches to ensure players guard against precisely the same slip by which Chris Smalling allowed Vincent Kompany to give him the slip, 15 days ago.
Mancini's judgement should not be overlooked amid all the spending. Last summer, he outbid Ferguson on Nasri and was not interested in Ashley Young, a player whose abilities were pressed on him by some of his staff. That looks like a good call. This season has seen him richly repaid for the investment of faith in goalkeeper Joe Hart which his predecessor, Mark Hughes, never showed. Ferguson has admitted Hart is one United allowed to pass by.
Mancini has passed the tactical test, too. The first-team coach of a then top six side told me in December that clubs had worked out how to strangle a then buoyant City and those words proved to be prophetic. A few days later, West Bromwich Albion dug in for a Boxing Day draw against City at the Hawthorns. Other clubs followed suit. Mancini has mapped a course between the expressive football of the season's first six months, playing 4-4-2, and the temptation to revert to something more defensive – 4-5-1.
The new champions' former chief executive, Garry Cook, who has done as much as anyone to deliver the club to today's pinnacle, has pored over Ferguson's biography and once took the chance to quiz him on his formative years running a pub in Glasgow's Gorbals.
"I respect that man probably more than anyone else in football," Cook once told me. But in the end, it was the money – the options it delivered, like a £38m striker called Sergio Aguero – that talked.
Manchester City: man-for-man marking
A quiet day except for the two goals. Would have done very well to save Djibril Cissé's strike, and could not have stopped Mackie's header. 6/10
Must have thought that his goal had won the title in an easier way. Put in a typically selfless performance tracking up and down the right flank, but could not provide the necessary second-half incision. 6
A very useful outlet down the left wing all afternoon, stretching the play and sending in crosses of mixed quality. Defensively good enough, absolved of blame for the goals. 6
Must have feared that he was responsible for City losing the title. His misjudgement of a simple header let in Cissé for the equaliser. 5
Slow for Mackie's goal, but must have wondered what more he could have done after an immaculate season looked to be ending trophyless. 5
Smart movement throughout, but he could not pick the holes in Rangers' massed defence. Saw enough of the ball but could not do enough with it until the end. 6
City's great physical threat went off in the first half, denying them a presence that they could have done with early on in a frenetic second half. 5
This was never really a game for him: QPR's two goals came well behind him and he was not the man to re-pick the lock. Withdrawn for Edin Dzeko in the second half. 5
Prompted some of City's better moves in the first half but when QPR were ahead he struggled to create the openings the home side needed before the very end. 6
One of the best strikers in the world, he made an impact when it mattered most. Quiet for 94 minutes before one of the most important interventions in English football history. 8
Tried to string together City's first-half moves, showing for the ball and holding it up, but without the necessary impact. Went off when it looked lost, but gets a medal. 5
Best off the bench
Dzeko might not be at City next season, but who cares? He is always an aerial threat and his late header built the platform for Aguero's historic winner. 7
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